Xerogels and aerogels are special classes of low-density open-cell foams with large internal void fractions (i.e. porosity). This leads to useful material properties such as high surface area to volume ratios, low thermal conductivity (2-3 orders of magnitude less than silica glass), and high acoustic impedance. Correspondingly, these materials have been used in applications such as thermal and acoustic insulation, catalysis, gas filters, gas storage, electrodes for electrochemical devices such as super capacitors and batteries, as well as micro fluidics to name a few.